Treatment premises of different types, in particular so-called paint spray booths for spray painting e.g automobile chasses, principally because of their spaciousness and furthermore because of the necessity for an effective ventilation, require great quantities of heated air. In today's burdensome cost situation, in particular thermal energy cost, the heated air must be utilized for the recovery of as much heat as possible.
Toward this objective, prior installations up to now allowed the cold supply air and the warm exhaust air meet in a heat exchanger, which naturally results in certain savings of energy. The exhaust air however not only is heated, but also is humidified, so that for example during wintertime, grave problems arise due to freezing insuch a heat exchanger. If the exhaust air contains pollutants, serious filtration and blockage problems can occur. Since both mediums are gaseous, poor thermal transfer characteristics moreover result, requiring relatively large and expensive heat exchangers.